C-S bond cleavage of benzo[b]thiophene at ruthenium

Article abstract of DOI:10.1021/om980051t

The ruthenium(II) (tetrahydroborate)hydride complex [(triphos)RuH(BH₄)] (1) reacts with benzo[b]thiophene (BT) in THF at 40 °C yielding, after 3 h, a mixture of four different compounds: [(triphos)RuH{BH₃(o-S(C₆H₄)CH ₂CH₃)}] (2), [(triphos)Ru{η⁴-S(C₆H₄)CH(CH₃)}] (3), [(triphos)RuH(μ-S(C₆H₄)CH₂CH ₃)₂HRu(triphos)] (4), and [(triphos)RuH(μ-BH₄)HRu-(triphos)]⁺ (5⁺) (triphos = MeC(CH₂PPh₂)₃). After two further hours of reaction, 3 disappears and is completely converted to 4. Further heating at 40 °C does not change the product composition (2, 4, and 5⁺ in a 4:1.3:3 ratio). A variety of independent reactions with isolated compounds have been performed with the aim of elucidating the mechanism of the C-S insertion/hydrogenation of BT to the 2-ethylthiophenolate ligand. The μ-thiolate complex 4 reacts in THF with dihydrogen (≥160 °C, 30 bar H₂) or with HBF₄·OEt₂ (20 °C) yielding ethylbenzene and 2-ethylthiophenol, respectively. No reaction occurs with LiHBEt₃. All of the reactions and new complexes reported have been studied by multinuclear NMR spectroscopy. An X-ray analysis has been carried out on a single crystal of 2.

Full text of DOI:10.1021/om980051t

Organometallics 1998, 17, 2495-2502
2495
C-S Bon d Clea va ge of Ben zo[b]th iop h en e a t Ru th en iu m
Claudio Bianchini,* Dante Masi, Andrea Meli, Maurizio Peruzzini,
Francesco Vizza, and Fabrizio Zanobini
Istituto per lo Studio della Stereochimica ed Energetica dei Composti di Coordinazione,
ISSECC-CNR, Via J . Nardi 39, I-50132 Firenze, Italy
Received J anuary 27, 1998
The ruthenium(II) (tetrahydroborate)hydride complex [(triphos)RuH(BH4)] (1) reacts with
benzo[b]thiophene (BT) in THF at 40 °C yielding, after 3 h, a mixture of four different
compounds: [(triphos)RuH{BH3(o-S(C6H4)CH2CH3)}] (2), [(triphos)Ru{η4-S(C6H4)CH(CH3)}]
(3), [(triphos)RuH(µ-S(C6H4)CH2CH3)2HRu(triphos)] (4), and [(triphos)RuH(µ-BH4)HRu-
(triphos)]+ (5+) (triphos ) MeC(CH2PPh2)3). After two further hours of reaction, 3 disappears
and is completely converted to 4. Further heating at 40 °C does not change the product
composition (2, 4, and 5+ in a 4:1.3:3 ratio). A variety of independent reactions with isolated
compounds have been performed with the aim of elucidating the mechanism of the C-S
insertion/hydrogenation of BT to the 2-ethylthiophenolate ligand. The µ-thiolate complex 4
reacts in THF with dihydrogen (g160 °C, 30 bar H2) or with HBF4‚OEt2 (20 °C) yielding
ethylbenzene and 2-ethylthiophenol, respectively. No reaction occurs with LiHBEt3. All of
the reactions and new complexes reported have been studied by multinuclear NMR
spectroscopy. An X-ray analysis has been carried out on a single crystal of 2.
In tr od u ction
bypassed. To this end, model studies applying soluble
ruthenium complexes might contribute to elucidate the
mechanisms through which ruthenium interacts with
the various types of thiophenic substrates as well as the
other contaminants in fossil fuels (nitrogen and oxygen
heterocycles, metal compounds). Despite many recent
research efforts in this direction,4 information on the
reactivity of ruthenium complexes toward thiophenic
substrates is still scarce and essentially limited to the
reactions with thiophene (T). Both C-H5 and C-S6,7
bond cleavage reactions of T have been reported to take
place at ruthenium. However, in no case has the
rupture of T been observed to occur by direct C-S
insertion of ruthenium. In the known examples, C-S
bond cleavage has invariably been achieved by action
of either nucleophiles on Ru(II) η5-T complexes6,7a,b or
electrophiles on Ru(0) η4-T complexes.7c,d The reactions
between ruthenium complexes and fused-ring thiophenes
such as benzo[b]thiophene (BT) or dibenzo[b,d]thiophene
(DBT) have received even less attention than those with
T.4 To the best of our knowledge, only one example of
Hydrodesulfurization (HDS) catalysis is the process
of removing sulfur as H2S from crude petroleum to
provide more processable and environmentally sound
fuels. The HDS reaction is accomplished by means of
heterogeneous molybdenum (or tungsten) sulfide cata-
lysts which incorporate small amounts of sulfided late
transition metals acting as promoters.1 Among the
transition-metal promoters, ruthenium forms the most
active sulfide for the HDS of thiophenes,2 but Ru-
promoted catalysts are scarcely employed in actual
hydrotreating reactors due to their facile poisoning.1
Currently, industrial HDS catalysts almost invariably
contain cobalt or nickel as promoters (Co(Ni)-Mo(W)-S
phases).
On the basis of several model reactor studies2 and the
fact the Ru-Mo-S interaction phase is similar to the
largely employed Co-Mo-S phase,1,3 ruthenium might
have great potential as a HDS promoter once the factors
that are responsible for the deactivation of the catalysts
in refining conditions are understood and hopefully
(4) (a) Bianchini, C.; Meli, A. In Applied Homogeneous Catalysis with
Organometallic Compounds; Cornils, B., Herrmann, W. A., Eds.;
VCH: Weinheim, 1996; Vol. 2, p 969. (b) Bianchini, C.; Meli, A. J .
Chem. Soc., Dalton Trans. 1996, 801. (c) Angelici, R. J . Bull. Soc. Chim.
Belg. 1995, 104, 265. (d) Angelici, R. J . In Encyclopedia of Inorganic
Chemistry; King, R. B., Ed.; J ohn Wiley: New York, 1994; Vol. 3, p
1433. (e) Sa´nchez-Delgado, R. A. J . Mol. Catal. 1994, 86, 287. (f)
Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 39, 259. (g) Angelici, R. J .
Coord. Chem. Rev. 1990, 105, 61. (h) Angelici, R. J . Acc. Chem. Res.
1988, 21, 387.
(5) Bianchini, C.; Casares, J . A.; Osman, R.; Pattison, D. I.; Pe-
ruzzini, M.; Perutz, R. N.; Zanobini, F. Organometallics 1997, 16, 4611.
(6) (a) Hachgenei, J . W.; Angelici, R. J . Angew. Chem., Int. Ed. Engl.
1987, 26, 909. (b) Hachgenei, J . W.; Angelici, R. J . J . Organomet. Chem.
1988, 355, 359.
(1) (a) Topsøe, H.; Clausen, B. S.; Massoth, F. E. Hydrotreating
Catalysis; Springer-Verlag: Berlin, 1996. (b) Scherzer, J .; Gruia, A. J .
Hydrocracking Science and Technology; Marcel Dekker: New York,
1996. (c) Gates, B. C. Catalytic Chemistry; J ohn Wiley: New York,
1992; Chapter 5, p 390. (d) Prins, R.; deBeer, V. H. J .; Somorjai, G. A.
Catal. Rev.-Sci. Eng. 1989, 31, 1. (e) van den Berg, J . P.; Lucien, J . P.;
Germaine, G.; Thielemans, G. L. B. Fuel Proc. Technol., 1993, 35, 119.
(2) (a) Pecoraro, T. A.; Chianelli, R. R. J . Catal. 1981, 67, 439. (b)
Harris, S.; Chianelli, R. R. in Theoretical Aspects of Heterogeneous
Catalysis; Moffat, J . B., Ed.; van Nostrand Reinhold Catalysis Series;
van Nostrand Rheinhold: New York, 1990; p 206. (c) Chianelli, R. R.
Catal. Rev.-Sci. Eng. 1984, 26, 361. (d) Topsøe, H.; Clausen, B. S.;
Topsøe, N.-J .; Hyldoft, J .; Nørskov, J . K. Prepr.-Am. Chem. Soc., Div.
Pet. Chem. 1993, 38, 638. (e) Topsøe, H.; Clausen, B. S.; Topsøe, N.-J .;
Nørskov, J . K.; Ovesen, C. V.; J acobsen, C. J . H. Bull. Soc. Chim. Belg.
1995, 104, 283. (f) Kasztelan, S. Appl. Catal. A 1992, 83, L1. (g) Xiao,
F.-S.; Xin, Q.; Guo, X.-X. Appl. Catal. A 1993, 95, 21.
(7) (a) Krautscheid, H.; Feng, Q.; Rauchfuss, T. B. Organometallics
1993, 12, 3273. (b) Feng, Q.; Rauchfuss, T. B.; Wilson, S. R. Organo-
metallics 1995, 14, 2923. (c) Luo, S.; Rauchfuss, T. B.; Gan, Z. J . Am.
Chem. Soc. 1993, 115, 4943. (d) Dailey, K. M.; Rauchfuss, T. B.;
Rheingold, A. L.; Yap, G. P. A. J . Am. Chem. Soc. 1995, 117, 6396.
(3) Mitchell, P. C. H.; Scott, C. E. Bull. Soc. Chim. Belg. 1984, 93,
619.
S0276-7333(98)00051-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/15/1998

2496 Organometallics, Vol. 17, No. 12, 1998
Bianchini et al.
C-S insertion of BT has been reported so far.8 The
scarcity of experimental data and the potential of
ruthenium in HDS catalysis prompted us to carry out
a systematic study of the interactions between ruthe-
nium complexes and thiophenic molecules.
After many efforts, we have been able to find a soluble
ruthenium(II) complex which is capable of cleaving BT
without the cooperation of either a multimetallic struc-
ture or externally added reagents. This complex is the
(tetrahydroborate)hydride derivative [(triphos)RuH-
(BH4)]9 (1), which straightforwardly transforms BT into
the 2-ethylthiophenolate ligand. A detailed account of
this reaction and of further studies aimed at mimicking
the HDS of BT are also reported here.
was charged first with a solid sample of [(triphos)RuH(BH4)]
(1) (30 mg, 0.04 mmol) and then with a solution containing a
5-fold excess of BT (27 mg, 0.2 mmol) in THF-d8 (1 mL) under
nitrogen. After 2 freeze/pump/thaw cycles at -196 °C, the tube
was flame sealed and then placed into a NMR probe at room
temperature. The reaction was followed by variable-temper-
1
ature 31P{1H} and H NMR spectroscopy. No reaction between
1 (unresolved AM2 pattern at 14.6 and 59.1 ppm)9 and BT
occurred at room temperature within 1 h, while appreciable
formation of the µ-BH4 dimer [(triphos)RuH(µ-BH4)HRu-
(triphos)]+ (5+) (singlet at 40.9 ppm)11 took place. At 40 °C,
the amount of 5+ sligthly increased and the new complex
[(triphos)RuH{BH3(o-S(C6H4)CH2CH3)}] (2) was already ob-
1
served in the first 31P{1H} and H NMR spectra (31P{1H} NMR
AMQ spin system, δ 51.6 (dd, J (PAPM) ) 39.5 Hz, J (PAPQ) )
1
23.4 Hz, PA), 44.4 (dd, J (PMPQ) ) 23.4 Hz, PM), 8.9 (t, PQ); H
NMR δ 3.13 (dq, J (HH) ) 14.9, 7.5 Hz, CHH′CH3), 2.71 (dq,
J (HH) ) 14.9, 7.5 Hz, CHH′CH3), 2.7-2.1 (m, CH2P), 1.58 (q,
J (HP) ) 2.6 Hz, CH3), 1.20 (t, J (HH) ) 7.5 Hz, CHH′CH3),
-7.45 (dt, J (HPtrans) ) 96.8 Hz, J (HPcis) ) 18.7 Hz, Ru-Ht),
-8.45 (br, Ru-H-B)). Compound 2 was identified by com-
parison of its 31P{1H} and 1H NMR spectra to those of an
authentic specimen (see below). Subsequent 31P{1H} NMR
spectra acquired within 3 h at a constant temperature of 40
°C showed a seemingly simple scenario. Complex 1 gradually
disappeared, formed in its place were 2 and 5+. 1H NMR
spectroscopy showed, however, that the reaction between 1 and
BT is much more complicated than it was apparent from the
31P{1H} NMR spectra. Indeed, at least two other ruthenium
complexes were formed during the reaction, which were not
detected by 31P{1H} NMR spectroscopy due to their high
fluxionality on the 31P NMR time scale. At 40 °C, the
resonances of these products, which have been assigned the
formulas [(triphos)Ru{η4-S(C6H4)CH(CH3)}] (3) and [(triphos-
)RuH(µ-S(C6H4)CH2CH3)2HRu(triphos)] (4), respectively (vide
infra), are in fact completely merged into the baseline (see
below). The formation of 3 and 4 in the course of the reaction
between 1 and BT was unambiguously shown by 1H NMR
spectroscopy (Figure 1). A quintet at δ -1.15 (J (H,H/P) ) 5.3
Hz), attributed to the CH(CH3) methyl hydrogens of the sulfur
ligand in 3, already appeared in the first 1H NMR spectra
(traces a, b). The amount of 3 increased with time, reaching
its maximum after 3 h (trace c). At this stage of the reaction,
a quartet at δ -1.35 (J (HP) ) 20.6 Hz) due to the terminal
hydrides in the dimeric complex 4 (see below) began to be
visible (trace c). With time, the concentration of 3 decreased
and concomitantly that of 4 increased (traces d, e). After 5 h
at 40 °C, only 2, 4, and 5+ were detected in the reaction
mixture (trace f). No change in the concentration of 4 was
Exp er im en ta l Section
Gen er a l In for m a tion . All reactions and manipulations,
except as stated otherwise, were routinely performed under a
nitrogen atmosphere by using standard Schlenk techniques.
High-temperature reactions and reactions under a controlled
pressure of hydrogen were performed with a stainless steel
Parr 4565 reactor equipped with a Parr 4842 temperature and
pressure controller. The ruthenium complex [(triphos)RuH-
(BH4)] (1) was prepared as previously described.9 All of the
isolated metal complexes were collected on sintered-glass frits
and washed with appropriate solvents before being dried in a
stream of nitrogen. Tetrahydrofuran (THF) and THF-d8 were
purified by distillation under nitrogen from LiAlH4. Benzo-
[b]thiophene (99%, Aldrich) was sublimed prior to use. 2-Eth-
ylthiophenol (90%), HBF4‚OEt2 (85% solution in OEt2), and
BH3‚THF (1.0 M solution in THF) were purchased from Aldrich
and used without further purification. All of the other
reagents and chemicals were reagent grade and used as
received by commercial suppliers. 1H (200.13 MHz), 13C{1H}
(50.32 MHz), and 31P{1H} (81.01 MHz) NMR spectra were
obtained on a Bruker ACP 200 spectrometer. All chemical
shifts are reported in ppm (δ) relative to tetramethylsilane,
referenced to the chemical shifts of residual solvent resonances
(1H, 13C) or 85% H3PO4 (31P). Broad-band and selective 1H-
{31P} NMR experiments were carried out on the Bruker ACP
200 instrument equipped with a 5-mm inverse probe and a
1
BFX-5 amplifier device. 13C-DEPT and H,1H 2D-COSY NMR
experiments were conducted on the Bruker ACP 200 spec-
trometer. 1H{11B} and 1H{31P} NMR experiments on 2 were
conducted on a Bruker Avance DRX 500 spectrometer using
the decoupling sequence GARP. The 11B{1H} NMR spectrum
of 2 was acquired on the same instrument oprerating at 160.47
MHz and calibrated against external NaBPh4 in acetone-d6
with downfield values taken as positive. The 10 mm sapphire
NMR tube was purchased from Saphikon, Milford, NH, while
the titanium high-pressure charging-head was constructed at
the ISSECC-CNR (Firenze, Italy).10 Note: Since high gas
pressures are involved, safety precautions must be taken at all
stages of studies involving high-pressure NMR tubes. GC
analyses were performed on a Shimadzu GC-14 A gas chro-
matograph equipped with a flame ionization detector and a
30 m (0.25 mm i.d., 0.25 µm film thickness) SPB-1 Supelco
fused silica capillary column. GC/MS analyses were performed
on a Shimadzu QP 5000 apparatus equipped with a column
identical with that used for GC analyses. Infrared spectra
were recorded on a Perkin-Elmer 1600 Series FT-IR spectro-
photometer using samples mulled in Nujol between KBr
plates.
observed for
a further 1 h heating. At the end of the
experiment, 2, 4, and 5+ were detected in the ratios of 4:1.3:3
(based on 1H NMR integration of the methyl resonance of
triphos).
Several experiments were carried out in different conditions.
(A) In the presence of an excess of (NMe4)BH4, the reaction
between 1 and BT was faster and gave a 3:1 mixture of 2 and
4 in ca. 1 h. The dimer 5+ was formed in trace amounts (1-
2%).
(B) When the reaction was carried out under 5 bar of H2, 3
was never seen by NMR prior to the formation of 4. After 3
h, compounds 2, 4, and 5+ were formed in a ca. 5:1:3 ratio.
(C) Only compounds 2 and 5+ in a 2:1 ratio were obtained
when the reaction was performed in the presence of both H2
(5 bar) and BH3‚THF (5-fold excess).
(D) Neither 4 nor 3 was seen when a 5-fold excess of BH3‚-
THF was added to the initial reaction mixture. After 3 h of
Rea ction s of [(Tr ip h os)Ru H(BH4)] (1) w ith Ben zo[b]-
th iop h en e (BT). In Situ NMR Stu d ies. A 5 mm NMR tube
(10) CNR (Bianchini, C.; Meli, A.; Traversi, A.) Italian Patent FI
A000025, 1997.
(11) Rhodes, L. F.; Venanzi, L. M.; Sorato, C.; Albinati, A. Inorg.
Chem. 1986, 25, 3335.
(8) Arce, J . A.; De Sanctis, Y.; Karam, A.; Deeming, J . A. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1381.
(9) Rhodes, L. F.; Venanzi, L. M. Inorg. Chem. 1987, 26, 2692.

C-S Bond Cleavage of Benzo[b]thiophene at Ru
Organometallics, Vol. 17, No. 12, 1998 2497
F igu r e 2. Variable-temperature 31P{1H} NMR study
(THF-d8, 81.01 MHz) of the thermal conversion of 2 to 4:
(a) at room temperature; (b) at 80 °C; (c) at 80 °C for 1 h;
(d) at 80 °C for 4 h.
F igu r e 1. 1H NMR study (THF-d8, 200.13 MHz) of the
reaction between 1 and BT at 40 °C: (a) after 0.5 h; (b)
after 1 h; (c) after 3 h; (d) after 3.5 h; (e) after 4 h; (f) after
5 h.
Ru-H-B). 1H{11B} NMR (CD2Cl2, 2 °C): δ 1.95 (br, B-H),
-7.55 (dt, J (HPtrans) ) 96.5 Hz, J (HPcis) ) 18.9 Hz, Ru-H),
-8.55 (br d, J (HP) ) 33.5 Hz, Ru-H-B). 11B{1H} NMR (CD2-
Cl2, 2 °C): δ -17.78 (br s, w1/2 ) 380 Hz). 13C{1H} NMR (CD2-
Cl2, 20 °C): δ 27.9 (s, CH2CH3), 15.4 (s, CH2CH3). IR: ν(B-
heating at 40 °C, complexes 2 and 5+ were formed in a ca. 2:1
ratio.
Ht) 2423 (m), 2399 (s); ν(B-Hb) + ν(Ru-Ht) 1927 (br, m) cm-1
.
(E) The selective formation of 2 occurred when the reaction
between 1 and BT was carried out in the presence of a 5-fold
excess of both (NMe4)BH4 and BH3‚THF.
B. A THF (10 mL) solution of 2-ethylthiophenol (ETP) (60
µL, 0.4 mmol) was slowly added to a stirred solution of 1 (300
mg, 0.4 mmol) in THF (20 mL) at room temperature under
nitrogen. After 30 min, the addition of ethanol (30 mL),
followed by partial evaporation of the solvents under a steady
stream of nitrogen, led to the precipitation of 2 in 85% yield.
NMR Ch a r a cter iza tion of [(Tr ip h os)Ru {η4-S(C6H4)CH-
(CH3)}] (3). In an independent NMR experiment, carried out
as described above, the tube was removed from the spectrom-
eter when the amount of 3 reached its maximum (ca. 3 h).
The tube was cooled to 0 °C and then reintroduced into the
NMR probe at 0 °C. 1H, 31P{1H}, and 1H{31P} NMR spectra
were acquired in the temperature range from 0 to -60 °C. In
this temperature range, 3 gave rise to a well-resolved 31P AMQ
spin system at -40 °C. 31P{1H} NMR (THF-d8, -40 °C): AMQ
spin system, δ 42.8 (dd, J (PAPM) ) 42.5 Hz, J (PAPQ) ) 18.6
Hz, PA), 33.8 (dd, J (PMPQ) ) 26.1 Hz, PM), 13.1 (dd, PQ). 1H
NMR (THF-d8, 0 °C): δ 2.95 (q, 1H, J (HH) ) 5.7 Hz, CHCH3),
2.6-2.2 (m, 6H, CH2P), 1.59 (q, 3H, J (HP) ) 2.6 Hz, CH3),
-1.18 (quint, 3H, J (HH) ) 5.7 Hz, J (HP) ) 5.1 Hz, CHCH3).
1H{31P} NMR (THF-d8, 0 °C): δ 2.95 (q, 1H, J (HH) ) 5.7 Hz,
CHCH3), -1.18 (d, 3H, J (HH) ) 5.7 Hz, CHCH3).
Th er m a l Con ver sion of 2 to [(Tr ip h os)Ru H(µ-S(C6H4)-
CH2CH3)2HRu (tr ip h os)] (4). A. NMR Exp er im en t. A 5
mm NMR tube was charged with a THF-d8 solution (1 mL) of
2 (30 mg, 0.034 mmol) under nitrogen. After 2 freeze/pump/
thaw cycles at -196 °C, the tube was flame sealed and then
placed into a NMR probe at room temperature. The reaction
was followed by variable-temperature 31P{1H} and 1H NMR
spectroscopy. A sequence of selected 31P{1H} NMR spectra is
reported in Figure 2.
Compound 2 (trace a) was found to convert to 4 only when
the probe head was heated to 80 °C (trace b); quantitative
conversion occurred in ca. 4 h (trace d). Afterward, the
temperature of the probe head was decreased to 60, 40, 20, 0,
Syn th esis of [(Tr ip h os)Ru (H){BH3(o-S(C6H4)CH2CH3)}]
(2). A. A mixture of 1 (300 mg, 0.4 mmol) and a 5-fold excess
of BT (270 mg, 2 mmol) in THF (50 mL) was heated at 40 °C
for 3 h with stirring. The resulting orange solution was
concentrated to dryness. A portion of the residue, dissolved
1
-20, -40, and -60 °C and 31P{1H} and H NMR spectra were
acquired at each temperature (Figure 3).
At 80 °C, the spectrum showed a unique broad signal
centered at ca. δ 48.9, which is consistent with the fast
exchange of the three phosphorus atoms of each triphos in the
dimeric molecule (trace a). Decreasing the temperature to 60
°C resulted in the extensive broadening of the signal (trace
b), which merged into the baseline below 40 °C (traces c, d).
Decoalescence occurred above 0 °C. At -20 °C, an AM2 pattern
was clearly visible (trace e), which was completely resolved at
-60 °C (trace f): δ 68.6 (d, J (PAPM) ) 18.3 Hz, PA), 13.9 (t,
PM). In the 1H NMR spectra, the resonance of the terminal
hydride ligands appeared as a quartet in the temperature
range from 80 to 20 °C and a well-resolved doublet of triplets
at -60 °C. 1H NMR (20 °C): δ 3.20 (q, 4H, J (HH) ) 7.5 Hz,
CH2CH3), 2.48 (d, 12H, J (HH) ) 8.1 Hz, CH2P), 1.75 (q, 6H,
J (HP) ) 2.7 Hz, CH3), 1.45 (t, 6H, J (HH) ) 7.5 Hz, CH2CH3),
-1.31 (q, 2H, J (HP) ) 20.8 Hz, Ru-H). 1H NMR (-60 °C): δ
-1.11 (dt, 2H, J (HPtrans) ) 97.7 Hz, J (HPcis) ) 36.9 Hz, Ru-
H).
1
in THF-d8 and analyzed by 31P{1H} and H NMR spectroscopy,
was found to contain 2, 4, and 5+ in ratios quite comparable
to those observed in the corresponding NMR experiment. The
rest of the residue was recrystallized from THF/ethanol to give
2 as well-shaped off-white crystals in 55% yield. Anal. Calcd
(found) for C49H52BP3RuS: C, 67.04 (66.81); H, 5.97 (5.89); Ru,
11.51 (11.31). 31P{1H} NMR (CD2Cl2, 20 °C): AMQ spin
system, δ 50.6 (dd, J (PAPM) ) 39.7 Hz, J (PAPQ) ) 23.1 Hz,
PA), 44.2 (dd, J (PMPQ) ) 23.1 Hz, PM), 9.7 (t, PQ). 1H NMR
(CD2Cl2, 20 °C): δ 2.96 (dq, 1H, J (HH) ) 14.9 Hz, J (HH) )
7.5 Hz, CHH′CH3), 2.61 (dq, 1H, J (HH) ) 14.9 Hz, J (HH) )
7.5 Hz, CHH′CH3), 2.55-1.95 (m, 6H, CH2P), 1.47 (q, 3H,
J (HP) ) 2.7 Hz, CH3), 1.10 (t, 3H, J (HH) ) 7.5 Hz, CHH′CH3),
-7.55 (dt, 1H, J (HPtrans) ) 96.5 Hz, J (HPcis) ) 18.9 Hz, Ru-
H), -8.55 (br, 1H, w1/2 ) 72 Hz, Ru-H-B). 1H{31P} NMR
(CD2Cl2, 20 °C): δ -7.55 (s, Ru-H), -8.55 (br, w1/2 ) 44 Hz,

2498 Organometallics, Vol. 17, No. 12, 1998
Bianchini et al.
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for 2
formula
mw
C49H52BP3RuS
877.83
cryst size, mm
cryst syst
space group
a, Å
0.075 × 0.1 × 0.55
triclinic
P1h
10.206(5)
b, Å
13.760(5)
c, Å
16.526(5)
R, deg
â, deg
γ, deg
V, Å3
91.530(5)
103.010(5)
104.980(5)
2175.5(15)
Z
F
2
calcd, g cm-3
1.340
0.540
914
abs coeff, mm-1
F(000)
radiation, Å
θ range, deg
index ranges
Mo, 0.710 69
2.54-21.97
-10 e h e 10, -14 e k e 14,
0 e l e 17
no. of reflns collected
no. of indep reflns
refinement method
5532
5306 (Rint ) 0.0264)
full-matrix least squares on F2
5306/0/177
data/restraints/param
goodness of fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.019
R1 ) 0.0582, wR2 ) 0.1351
R1 ) 0.0965, wR2 ) 0.1513
0.862
F igu r e 3. Variable-temperature 31P{1H} NMR spectra
(THF-d8, 81.01 MHz) of 4: (a) 80 °C; (b) 60 °C; (c) 40 °C;
(d) 0 °C; (e) -20 °C; (f) -60 °C.
largest diff peak, e Å-3
largest diff hole, e Å-3
-0.507
those reported by Cromer and Waber12 with an anomalous
dispersion correction taken from ref 13. Absorption correction
was applied via ψ scan. All calculations were done on a
DIGITAL DEC 2000 AXP workstation using the SHELX-97
program.14 Crystallographic details are reported in Table 1.
The structure was solved by direct methods using the SIR93
program.15 An empirical absorpion correction was applied via
ψ scans with transmission factors in the range 0.94-1.00.
Refinement was done by full-matrix least-squares calculations,
initially with isotropic thermal parameters and finally with
anisotropic thermal parameters for the Ru and P atoms. The
phenyl rings were treated as rigid bodies with D6h symmetry,
and hydrogen atoms were introduced at calculated positions.
The final difference map was featureless.
B. Syn th etic Exp er im en t. A THF solution (50 mL) of 2
(300 mg, 0.34 mmol) was heated in a Parr reactor at 80 °C
under nitrogen. After 5 h, the reactor was allowed to cool to
room temperature. The reaction mixture was transferred into
a Schlenk-type flask where it was concentrated to 5 mL in
vacuo. Portionwise addition of n-heptane (ca. 40 mL) led to
the precipitation of 4 as a yellow-orange solid, which was
filtered off and washed with n-pentane; yield 90%. Anal.
Calcd (found) for C98H98P6Ru2S2: C, 68.12 (67.33); H, 5.72
(5.71); Ru, 11.70 (11.12). IR: ν(Ru-H) 1900 (m) cm-1
.
Rea ction of 4 w ith BH3‚THF . NMR Exp er im en t. A 5
mm NMR tube was charged first with a THF-d8 solution (1
mL) of 4 (30 mg, 0.017 mmol) and then with a 10-fold excess
1
of BH3‚THF under nitrogen. The 31P{1H} and H NMR spectra
of this sample showed the quantitative conversion of 4 to 2 at
room temperature.
Resu lts a n d Discu ssion
Rea ction of 4 w ith HBF 4‚THF or LiHBEt3. NMR
Exp er im en t. A 5 mm NMR tube was charged first with a
THF-d8 solution (1 mL) of 4 (30 mg, 0.017 mmol) and then
with a 2-fold excess of HBF4‚THF under nitrogen. The 31P-
Ch a r a cter iza tion of th e New Com p lexes. Four
ruthenium complexes are produced upon the reaction
of 1 with BT in THF at 40 °C (Scheme 1). Of these
products, only [(triphos)Ru{η4-S(C6H4)CH(CH3)}] (3) has
a fleeting existence and, for this reason, has been
studied exclusively in solution. All of the other com-
pounds have been isolated and adequately characterized
in both the solid state and solution.
An X-ray analysis was carried out on a single crystal
of the mononuclear C-S insertion/hydrogenation prod-
uct [(triphos)RuH{BH3(o-S(C6H4)CH2CH3)}] (2). Figure
4 shows a ZORTEP view of the molecule, while crystal-
lographic data and selected bond distances and angles
are listed in Tables 1 and 2, respectively.
1
{1H} and H NMR spectra of this sample showed the quantita-
tive formation of free ETP (1H NMR δ 4.14 (s, SH), 2.78 (q,
J (HH) ) 7.4 Hz, CH2CH3), 1.31 (t, CH2CH3)) together with
some unidentified ruthenium species.
Substitution of LiHBEt3 for HBF4‚THF resulted in no
transformation of 4 up to 80 °C.
Rea ction of 4 w ith H2. The thermolysis of 4 in the
presence of H2 (30 bar) was carried out in THF solution in a
Parr reactor. No reaction occurred below 120 °C. At 160 °C,
the starting complex decomposed to give ethylbenzene and
traces of ETP (GC/MS analysis). No H2S was evolved. The
solvent was removed under reduced pressure, and the solid
residue was analyzed by NMR spectroscopy, which showed the
formation of several unidentified products.
The P3Ru grouping of the (fac-triphos)Ru fragment
has an approximate C3v symmetry with three P-Ru-P
X-r a y Da ta Collection a n d Str u ctu r e Deter m in a tion
of 2. Data were collected on a Enraf-Nonius CAD4 diffracto-
meter. Unit cell dimensions were determined from the least-
squares refinement of the angular settings of 25 carefully
centered reflections. Three standard reflections, checked every
2 h, showed no decay. Intensity data were corrected for
Lorentz-polarization effects. Atomic scattering factors were
(12) Cromer, D. T.; Waber, J . T. Acta Crystallogr. 1965, 18, 104.
(13) International Tables of Crystallography; Kynoch: Birmingham,
England, 1974; Vol. 4.
(14) Sheldrick, G. M. SHELX-97 Program for Structure Refinement;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(15) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 27,
435.

C-S Bond Cleavage of Benzo[b]thiophene at Ru
Organometallics, Vol. 17, No. 12, 1998 2499
Sch em e 1a
a
Reaction conditions: THF, 40 °C.
1
1
F igu r e 5. 1H, H{31P}, and H{11B} NMR spectra of 2 in
the -7/-9 ppm region (500.13 MHz, CD2Cl2, 2 °C).
similar to the Ru-S distance in the C-S-inserted 2,5-
dimethylthiophene complex [CpRu(PPh2Me)2{η1-SC-
(Me)dCHCHd(Me)}] (2.44(6) Å).6b No bonding inter-
action is envisaged between the Ru and B atoms
(2.473(9) Å).16 Neither the terminal hydride nor the
bridging and terminal hydrogen atoms of the tetrahy-
droborate ligand could be located by X-ray diffraction.
The presence and position of all of these hydrogen atoms
have unambiguously been determined by NMR spec-
troscopy, however.
F igu r e 4. ZORTEP drawing of [(triphos)Ru(H){BH3(o-
S(C6H4)CH2CH3)}] (2). Phenyl rings of triphos are omitted
for clarity.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 2
Distances
Ru(1)-P(3)
Ru(1)-P(1)
Ru(1)-P(2)
Ru(1)-S(1)
S(1)-B(1)
2.251(2)
2.266(2)
2.359(2)
2.428(2)
1.911(9)
Complex 2 is stereochemically rigid on the NMR time
scale up to 80 °C, at which temperature it starts
decomposing to give the dimer [(triphos)RuH(µ-S(C6H4)-
CH2CH3)2HRu(triphos)] (4) and BH3. The 31P{1H} NMR
spectrum consists of an AMQ pattern, typical of triphos
metal complexes in which three different ligands are
trans to the phosphorus donors. The terminal hydride
Angles
P(3)-Ru(1)-P(1)
P(3)-Ru(1)-P(2)
P(1)-Ru(1)-P(2)
P(3)-Ru(1)-S(1)
P(1)-Ru(1)-S(1)
P(2)-Ru(1)-S(1)
C(17)-S(1)-B(1)
C(17)-S(1)-Ru(1)
B(1)-S(1)-Ru(1)
86.23(8)
89.90(7)
90.60(7)
164.49(7)
104.30(8)
101.18(7)
107.7(4)
109.0(2)
68.3(3)
1
Ht (δ -7.55) appears as a doublet of triplets in the H
NMR spectrum and becomes a singlet in the phosphorus-
decoupled 1H{31P} spectrum (Figure 5). The position
of Ht trans to P(2) is suggested by the long Ru-P(2)
distance (2.359(2) Å) as well as the high-field 31P NMR
chemical shift of this phosphorus atom (9.7 ppm) (trans
influence of the hydride).17 The bridging Ru-H-B
hydrogen atom (Hb) falls at slightly higher field (δ
angles in the range 86.23(8)-90.60(7)°. The Ru-S bond
distance (2.428(2) Å) is comparable to those of ruthe-
nium-thiolate complexes,16 in particular, it is quite
(16) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1.
(17) Mason, R.; Meek, D. W. Angew. Chem., Int. Ed. Engl. 1978,
17, 183.

2500 Organometallics, Vol. 17, No. 12, 1998
Bianchini et al.
Sch em e 2
-8.55) than the terminal hydride and appears as a
hump (trace a) which becomes a broad doublet with a
J (HP) constant of 33.5 Hz in the 1H{11B} spectrum
(Figure 5). The selective boron-decoupled 1H NMR
spectrum also allows the localization of the B-H
hydrogens (δ 1.95) and unequivocally confirms our
assignment. The 11B{1H} NMR spectrum shows a
single, broad resonance at δ 17.78 which is typical of
BH4 ligands.18
-
Unlike 2, the identification of the dimers, 4 and
[(triphos)RuH(µ-BH4)HRu(triphos)]+ (5+) did not require
a long investigation. The µ-BH4 complex 5+ was straight-
forwardly authenticated by comparing its spectroscopic
characteristics with those reported in the literature by
Venanzi et al.11 A similar procedure was adopted to
identify 4 as it belongs to a family of (µ-thiolate)hydride
dimeric complexes of the formula [(triphos)MH(µ-
SR)2HM(triphos)]2+ (M ) Rh, Ir; R ) H,19 Me,19 C8H9,20
C12H9,21 C20H1322). In particular, 4 shares several
chemical-physical properties with the closely related
species [(triphos)IrH(µ-S(C6H4)CH2CH3)2HIr(triphos)]2+
similarly obtained by C-S insertion/hydrogenation of
BT.20 Like the numerous Rh and Ir congeners, 4 is
highly fluxional on the NMR time scale, the slow-
exchange regime being attained at ca. -60 °C (31P AM2
Sch em e 3
1
pattern; H doublet of triplets for the two equivalent
terminal hydrides). The dynamic behavior of this class
of dimeric compounds has been attributed to the flex-
ibility of the thiolate bridges.23
known complexes containing the S(C6H4)CH(CH3) ligand
are analogously formed by metal-assisted transforma-
tion of BT and convert to the corresponding (µ-o-
ethylthiophenolate) hydride dimers by treatment with
H2 (Scheme 2).20
On the basis of the spectroscopic and chemical evi-
dence summarized above, 3 may be assigned a structure
in which a fac-(triphos)Ru fragment is coordinated by
a S(C6H4)CH(CH3) ligand. The transient nature of 3
in the experimental conditions leading to its formation
does not allow one to discriminate between structures
I and II, however. For this reason, we prefer to
represent the thioligand in 3 with a delocalized elec-
tronic structure in all of the schemes reported in this
paper.
In situ NMR (Figure 1) and model reaction studies
(see below) clearly show that 3 is a precursor to 4 via
1
hydrogen uptake. Indeed, from a comparison of the H
NMR spectra of 3 and 4, one may readily realize that
one of the H atoms added to the former complex
generates a Ru-H bond while the other contributes to
the formation of an ethyl group as neither hydride nor
ethyl ligands are present in 3. 1H NMR spectroscopy,
in combination with 1H{31P} and selective H,H-homo-
nuclear decoupling NMR experiments, reveals the pres-
ence of a CH(CH3) group in 3 (quartet at δ 2.95 (CH)
and quintet at δ -1.18 (CH3, J (HH) ) 5.7 Hz, J (HP) )
5.1 Hz)). The chemical shifts and the magnetic coupling
pattern of this CH(CH3) grouping are typical of metal
complexes containing the ligand S(C6H4)CH(CH3) which,
depending on the metal oxidation state, may be formu-
lated as either cyclohexadienthione (I) or thiophenolate
(II) (Scheme 2).20,24 In either case, the complex would
be devoid of any symmetry which is consistent with the
observed 31P AMQ pattern for 3. Moreover, all of the
Mod el Rea ction s. Several independent reactions
have been carried out with the aim of confirming the
structural assignments made above as well as getting
insight into the mechanism of formation of the various
products. The results of this study are illustrated in
Schemes 1 and 3 and may be summarized as follows.
-
(i) The presence of an excess of BH4 anions inhibits
(18) (a) Gozum, J . E.; Wilson, S. R.; Girolami, G. S. J . Am. Chem.
Soc. 1992, 114, 9483. (b) Rodriguez, A.; Sabo-Etienne, S.; Chaudret,
B. Ann. Quı´m. Int. Ed. 1996, 131.
(19) Bianchini, C.; Meli, A. Inorg. Chem. 1987, 26, 4268.
(20) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Moneti, S.;
Herrera, V.; Sa´nchez-Delgado, R. A. J . Am. Chem. Soc. 1994, 116, 4370.
(21) Bianchini, C.; Casares, J . A.; J ime´nez, M. V.; Meli, A.; Moneti,
S.; Vizza, F.; Herrera, V.; Sa´nchez-Delgado, R. A. Organometallics
1995, 14, 4850.
(22) Bianchini, C.; Fabbri, D.; Gladiali, S.; Meli, A.; Pohl, W.; Vizza,
F. Organometallics 1996, 15, 4604.
(23) Mu¨ller, A.; Diemann, E. In Comprehensive Coordination Chem-
istry; Wilkinson, G., Gillard, R. D., McCleverty, J . A., Eds.; Pergamon
Press: New York, 1987; Vol. 2, Chapter 16.1.
(24) (a) Bianchini, C.; Frediani, P.; Herrera, V.; J ime´nez, M. V.; Meli,
A.; Rinco´n, L.; Sa´nchez-Delgado, R. A.; Vizza, F. J . Am. Chem. Soc.
1995, 117, 4333. (b) Bianchini, C.; Herrera, V.; J ime´nez, M. V.; Laschi,
F.; Meli, A.; Sa´nchez-Delgado, R.; Vizza, F.; Zanello, P. Organometallics
1995, 14, 4390. (c) Iretskii, A.; Adams, H.; Garcia, J . J .; Picazo, G.;
Maitlis, P. M. J . Chem. Soc., Chem. Commun. 1998, 61.
the formation of 5+ but does not avoid the formation of
4, which is conversely suppressed when BH3‚THF is
added to the starting mixture. (ii) The conversion of 1
to 5+ is a thermolytic process that occurs even in pure
THF. Once formed, however, the µ-BH4 dimer does not
regenerate monomer 1, even by treatment with a large
excess of BH4- anions,11 and is also inactive toward BT
in the range of temperatures investigated. (iii) The
-
selective formation of 2 takes place when both BH4
anions and BH3‚THF are added to the reaction mixture.
Moreover, the presence of either reagent accelerates the
C-S bond cleavage/hydrogenation reactions of BT. (iv)
In the presence of H2 (5 bar), the reaction between 1
and BT is complete in 3 h, yielding 2, 4, and 5+.

C-S Bond Cleavage of Benzo[b]thiophene at Ru
Organometallics, Vol. 17, No. 12, 1998 2501
Sch em e 4
Sch em e 5
Complex 3 is not intercepted by NMR spectroscopy. (v)
Complex 3 readily reacts with H2 to give 4. (vi) Complex
2 is thermally stable at 40 °C, thus it cannot generate
4 under the experimental conditions of the C-S inser-
tion reaction. Only at 80 °C does the thermolysis of 2
slowly give 4. (vii) Traces of free H2 have been detected
by 1H NMR spectroscopy (singlet at 4.7 ppm) in the
course of all reactions between 1 and BT.
whereas it is quite common for d8 metal complexes (e.g.
Rh(I) and Ir(I)).20,22,24a,b,26-28 If we, thus, assume that
BT binds ruthenium through the C2-C3 double bond
as shown in intermediate A, then the opening of BT
would follow the general mechanism which involves the
addition of electrophiles (in the case at hand BH3) to
the sulfur, followed by nucleophilic cleavage of the C-S
bond by the hydride ligand.27a,29 As an example,
Scheme 5 summarizes the formation of 4-(alkylthio)-
1,3-butadiene derivatives from Os(II) η2-thiophene com-
plexes reported by Harman and Spera.29a
The formation of intermediate C (BT-derived ana-
logues of this complex have precedents in the relevant
literature)21,24a,27a,e may proceed by either a stepwise (A
f Bf C) or concerted (A f C) process. Once formed,
C evolves to 2 via hydrogenation of the vinyl group in
the reducing environment of the reaction, which com-
prises BH4- anions generated by the partial conversion
of 1 to 5+ as well as H2. In competition with the
Rea ction betw een [(tr ip h os)Ru H(BH4)] a n d Ben -
zo[b]th iop h en e. As illustrated in Scheme 1, the
reaction between 1 and BT is a quite complex process.
However, with the contribution of in situ NMR spec-
troscopy, independent reactions using isolated com-
pounds as well as relevant precedents in the literature,
a rationalization of the chemical processes involved in
the present C-S insertion/hydrogenation of BT may be
proposed (Scheme 4).
In the mechanism reported in Scheme 4, a vacant
coordination site at ruthenium for the incoming BT
molecule is provided by the change of the bonding mode
of the tetrahydroborate ligand in 1 from η2 to η1. Such
hapticity changes have been invoked to account for both
the fluxionality of tetrahydroborato metal complexes
and their reactions with nucleophiles.25 Moreover, the
-
decoordination of the BH4 anion from 1, which ulti-
mately leads to the formation of 5+, occurs readily at
room temperature and reasonably proceeds via a step-
wise unfastening of the two Ru-H-B bonds. Once a
coordination vacancy has been created, BT may ap-
proach the metal center using either the sulfur atom or
the C2-C3 double bond.4,5 In the former case, direct
C-S bond cleavage might take place if the metal center
had sufficient electron density to be transferred into the
C-S π*orbital.4,26b This path has never been observed
for complexes with d6 metal ions (e.g., Ru(II)), however,
(27) (a) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Frediani,
P.; Herrera, V.; Sa´nchez-Delgado, R. A. J . Am. Chem. Soc. 1993, 115,
2731. (b) Bianchini, C.; J ime´nez, M. V.; Meli, A.; Moneti, S.; Vizza, F.;
Herrera, V.; Sa´nchez-Delgado, R. A. Organometallics 1995, 14, 2342.
(c) Bianchini, C.; J ime´nez, M. V.; Meli, A.; Moneti, S.; Vizza, F. J .
Organomet. Chem. 1995, 504, 27. (d) Bianchini, C.; J ime´nez, M. V.;
Meli, A.; Vizza, F. Organometallics 1995, 14, 3196. (e) Bianchini, C.;
J ime´nez, M. V.; Meli, A.; Vizza, F. Organometallics 1995, 14, 4858. (f)
Bianchini, C.; Herrera, V.; J ime´nez, M. V.; Meli, A.; Sa´nchez-Delgado,
R. A.; Vizza, F. J . Am. Chem. Soc. 1995, 117, 8567. (g) Bianchini, C.;
Meli, A.; Pohl, W.; Vizza, F.; Barbarella, G. Organometallics 1997, 16,
1517. (h) Bianchini, C.; Casares, J . A.; Masi, D.; Meli, A.; Pohl, W.;
Vizza, F. J . Organomet. Chem. 1997, 541, 143. (i) Bianchini, C.; Meli,
A.; Patinec, V.; Sernau, V.; Vizza, F. J . Am. Chem. Soc. 1997, 119,
4945. (j) Bianchini, C.; Casares, J . A.; Meli, A.; Sernau, V.; Vizza, F.;
Sa´nchez-Delgado, R. A. Polyhedron 1997, 16, 3099.
(25) (a) Bianchini, C.; Ghilardi, C. A.; Meli, A.; Midollini, S.;
Orlandini, A. Inorg. Chem. 1985, 24, 932. (b) Bianchini, C.; Ghilardi,
C. A.; Meli, A.; Midollini, S.; Orlandini, A. Inorg. Chem. 1985, 24, 924.
(26) (a) J ones, W. D.; Dong, L. J . Am. Chem. Soc. 1991, 113, 559.
(b) Dong, L.; Duckett, S. B.; Ohman, K. F.; J ones, W. D. J . Am. Chem.
Soc. 1992, 114, 151. (c) J ones, W. D.; Chin, R. M. J . Am. Chem. Soc.
1992, 114, 9851. (d) Chin, R. M.; J ones, W. D. Angew. Chem., Int. Ed.
Engl. 1992, 31, 357. (e) Myers, A. W.; J ones, W. D.; McClements, S.
M. J . Am. Chem. Soc. 1995, 117, 11704. (f) Myers, A. W.; J ones, W. D.
Organometallics 1996, 15, 2905.
(28) (a) Selnau, H. E.; Merola, J . S. Organometallics 1993, 12, 1583.
(b) Paneque, M.; Taboada, S.; Carmona, E. Organometallics 1996, 15,
2678.
(29) (a) Spera, M. L.; Harman, W. D. J . Am. Chem. Soc. 1997, 119,
8843. (b) Chen, J .; Angelici, R. J . Organometallics 1990, 9, 849.

2502 Organometallics, Vol. 17, No. 12, 1998
Bianchini et al.
Sch em e 6
hydrogenation step and formation of 2, C may convert
to 3 via hydride migration to the external carbon atom
of the double bond.20,24 This step involves the loss of
BH3, consistent with the fact that the addition of an
excess of BH3 to the initial reaction mixture totally
inhibits the formation of 3. Moreover, the elimination
of BH3 from 2 to give 4 has been proved experimentally.
Finally, hydrogenation of 3 yields the dimer 4 via the
electronically and coordinatively unsaturated species D.
Given the evident complexity of the reaction between
1 and BT, our mechanistic interpretation, though ac-
counting for all of the experimental observations, must
be considered with extreme caution. Many of the
proposed steps, if not all, however, are commonly
encountered in the reactions of soluble metal complexes
with thiophenes.
No reaction is observed when 4 is treated with
LiHBEt3, while ETP is liberated into the solution by
reaction with HBF4‚OEt2 at room temperature.
Con clu sion s
The position of ruthenium in the activity trends for
heterogeneous HDS is amply justified by the results
obtained in this work. Indeed, the hydrogenolysis of BT
assisted by 1 takes place in THF under reaction condi-
tions (40 °C, traces of H2), which are among the mildest
ever observed. In the proposed mechanism, the C-S
insertion step proceeds with the cooperation of both
electrophilic and nucleophilic agents, which is consistent
with several homogeneous and heterogeneous modeling
studies. In line with the model studies, it has also been
found that the multipoint coordination of the 2-ethylth-
iophenolate product is of crucial importance for the
desulfurization step, which, however, requires a drastic
increase in both temperature (g160 °C) and pressure
of H2 (30 bar) to occur.
Rea ction s of [(Tr ip h os)Ru H(µ-S(C6H4)CH2CH3)2-
HRu (tr ip h os)] w ith H+, H-, or H2. Several examples
of desulfurization of thiophenic substrates in fluid-phase
systems have been reported to occur by reaction of metal
complexes containing activated thiophenes with protic
acids, hydride-releasing compounds, or H2.27a,30-34 The
large majority of the homogeneous desulfurization reac-
tions proceed through thiolate ligands (hydrogenolysis
products), particularly when these bind simultaneously
to two or more metal centers.31-34 The rupture of the
C-S bond of µ-alkylthiolate ligands with consequent
formation of the desulfurized hydrocarbons and MdS
moieties generally takes place at elevated temperatures
and H2 pressures. Similarly, we have found that the
µ-o-ethylthiophenolate ligands are desulfurized to eth-
ylbenzene only by heating 4 in THF to g160 °C under
30 bar of H2 (Scheme 6).
Ack n ow led gm en t. A contract (PR1/C) from the
Ministero dell′Ambiente of Italy and an international
cooperation agreement between CNR (Italy) and CO-
NICIT (Venezuela) are gratefully acknowledged for
financial support.
(30) Garcia, J . J .; Mann, B. E.; Adams, H.; Bailey, N. A.; Maitlis, P.
M. J . Am. Chem. Soc. 1995, 117, 2179.
(31) Ogilvy, A. E.; Draganjac, M.; Rauchfuss, T. B.; Wilson, S. R.
Organometallics 1988, 7, 1171.
(32) (a) Bianchini, C.; J ime´nez, M. V.; Meli, A.; Moneti, S.; Patinec,
V.; Vizza, F. Organometallics 1997, 16, 5696. (b) Bianchini, C.; J ime´nez,
M. V.; Mealli, C.; Meli, A.; Moneti, S.; Patinec, V.; Vizza, F. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1706.
(33) (a) Vicic, D. A.; J ones, W. D. Organometallics 1997, 16, 1912.
(b) Vicic, D. A.; J ones, W. D. J . Am. Chem. Soc. 1997, 119, 10855. (c)
J ones, W. D.; Chin, R. M. J . Am. Chem. Soc. 1994, 116, 198.
(34) (a) Riaz, U.; Curnow, O. J .; Curtis, M. D. J . Am. Chem. Soc.
1994, 116, 4357. (b) Curtis, M. D.; Druker, S. H. J . Am. Chem. Soc.
1997, 119, 1027.
Su p p or tin g In for m a tion Ava ila ble: Tables of final
coordinates with equivalent isotropic thermal parameters
(Table S1), bond distances and angles (Table S2), anisotropic
thermal parameters (Table S3), and atomic coordinates of the
hydrogen atoms (Table S4) for 2 (6 pages). Ordering informa-
tion is given on any current masthead page.
OM980051T